The present invention is a process and apparatus for controlling the amount of condensable water in the vapor of multiple calcination or oxidation zones.
Moisture control is critical in a great variety of processes, and there are many techniques for measuring the moisture content in vapor. Popular techniques include spectroscopy and dew point sensors which sense a change in electrical capacitance due to condensation on the surface of a probe; see U.S. Pat. Nos. 5,123,277, 5,332,901, 5,357,441, and EP 0409546A2. However, measuring moisture in a vapor atmosphere becomes much more challenging when that atmosphere is at extremely high temperatures such as from 250xc2x0 C. to 1000xc2x0 C. At these extreme temperatures, capacitance probes and spectroscopic probes or flow cells fail. An Environmental Protection Agency method resorts to taking a portion of the vapor atmosphere and condensing any water present in the vapor; see 40 C.F.R. 60, App. A, Meth. 4. The amount of water condensed is either weighed or read volumetrically. Measurements by condensing and weighing or reading volumetrically in a graduated cylinder or burette require a significant sample size which may take an extensive period of time to collect. Also, manual weight or volumetric readings lack precision due to the subjectivity of the manual readings.
The present invention provides a technique and apparatus for controlling the moisture of the vapor phase in multiple zones of a high temperature calcination or oxidation operation which eliminate the subjectivity of the manual techniques. The unique design of the apparatus allows for accurate precise moisture measurements on a small sample size and the method of making those measurements provides steps for minimizing error. Furthermore, the small sample size needed allows for rapid determinations of multiple zones of an operation. The application of capacitance measurements as an analytical tool serves to eliminate subjectivity.
The purpose of the invention is to provide a process and apparatus for controlling the amount of water in the vapor of multiple zones of a calcination or to oxidation operation. The preferred apparatus contains a small volume vessel having a cooled condenser arm and a cooled collection chamber and is further equipped with a capacitance probe having a length extending into the collection chamber of the vessel. The condenser arm is connected to fluid conduits leading to each zone of a multizone calcination or oxidation operation. The process begins with calibrating the equipment and then adjusting the level of water in the collection chamber of a vessel so that from about 5 to about 15 percent of the length of the capacitance probe is immersed in the water and measuring and recording an initial capacitance, CI. A measured amount of vapor from a first zone is passed through the vessel in an amount sufficient to condense water into the collection chamber of the vessel. The vessel is purged with dry air for only such time as necessary to flush any droplets of water retained in the condenser arm of the vessel into the collection chamber of the vessel. A final capacitance, CF, is measured and recorded. The change in capacitance is calculated, xcex94C=(CFxe2x88x92CI), and the difference, xcex94C, is used along with the calibration to determine the amount of water condensed. With the amount of water condensed and the measured amount of vapor passed through the vessel, the amount of water in the vapor of the first zone may be readily calculated. An operating parameter of the calcination or oxidation process may be adjusted to bring or maintain the amount of water within a predetermined range. The process is repeated for additional zones.